The invention relates to the construction and operation of superconducting rotating machines, and more particularly to torque transmission assemblies for use in superconducting motors.
Superconducting electric machines have been under development since the early 1960s. The use of superconducting windings in these machines has resulted in a significant increase in the magnetomotive forces generated by the windings and increased flux densities in the machines. However, superconducting windings require cryogenic temperatures to operate properly. Thus, higher torque motors and generators are being developed to include mechanisms for transferring the torque between a rotor assembly and an output shaft while limiting heat transported to the cryogenic region of the machine.
The invention relates to rotor assemblies, as well as rotating machines (e.g., motor or generator) having such rotor assemblies. The rotor assembly is of the type configured to rotate within a stator assembly of the rotating machine and having a shaft disposed within a noncogenic region of the rotor assembly.
In one aspect of the invention, the rotor assembly includes at least one superconducting winding assembly positioned within a cryogenic region of the rotor assembly, and a cantilevered member, mechanically coupled between the at least one superconducting winding assembly and the shaft. The cantilevered member extends between the non-cryogenic region and cryogenic region of the rotor assembly. The at least one superconducting winding assembly, in operation, generates a magnetic flux linking the stator assembly.
Embodiments of this aspect of the invention may include one or more of the following features. The cantilevered member is positioned between the superconducting winding and the shaft (e.g., in the radial space between the superconducting winding and shaft). The cantilevered member extends along a longitudinal axis of the rotor assembly and has a length sufficient for providing substantial thermal isolation between the superconducting winding and the shaft. The rotor assembly also includes support member for supporting the at least one superconducting winding assembly. The support member and cantilevered member can be formed of the same material.
The cantilevered member is required to be formed of a high strength to thermal if conductivity ratio material including composites (e.g., S-glass, E-glass, carbon fiber). In certain embodiments, the cantilevered member is advantageously formed of a low thermal conductivity metal (e.g. Inconel 718, Ti6A14V).
The mechanical characteristics of the cantilevered member depend in large part on the size and rating of the rotor assembly. For example, a rotor assembly for use in a superconducting rotating machine rated at 25 MWatts has a cantilevered member having a thickness of 15 mm and a length within a range between 1200 mm and 1600 mm (e.g., 1390 mm). The cantilevered member is formed of a material the material having an elongation characteristic of at least 10 percent and a yield strength characteristic of at least 50 ksi. The material can have a stiffness ratio less than 20 nanoW*m/N and a strength ratio less than 5 microW*m/N, as will be defined in greater detail below.
Thus, the cantilevered member serves to effectively transfer torque from the rotor assembly while minimizing heat transfer between those components of the machine required to be cryogenically cooled (e.g., superconducting windings) and those parts of he machine that are not (e.g., shaft). This configuration provides a rotor assembly having an increased overall performance, particularly at relatively high torque, low speed conditions (e.g., less than 900 rpm and ratings greater than 2 MWatts).
For a metallic system, the cantilevered member is mechanically coupled to the support member with a weld joint. The superconducting windings include high temperature superconductor.
In certain embodiments, in order to simplify manufacture and reduce the number of weld joints, the cantilevered member and support member are formed of the same material. The rotor assembly further includes the high permeability member positioned between the shaft and the at least one superconducting winding, preferably between the shaft and support member. In such embodiments, the high permeability member serves to provide a lower reluctance path for the magnetic field generated by the superconducting windings.
In certain applications, the rotor assembly includes spokes for mechanically coupling the cantilevered member to the shaft. The spokes provide additional radial support to the support member to the superconducting winding assembly mounted to the support member. The cantilevered member can also include a bumper adapted to contact the shaft when the rotor assembly subjected to transverse shock.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.